French Pat. No. 2,276,872 proposed to prepare mono-crystals of HgI.sub.2 in an ampoule, maintained under vacuum, produed with the aid of a vacuum pump. The known system comprises three zones: a sublimation zone, containing a charge of polycrystalline HgI.sub.2, taken to a temperature sufficiently high for the latter to sublime in the vapor state; an intermediate transfer zone, taken to an essentially constant temperature, higher than that of the sublimation zone; and a zone for the growth of the mono-crystal of HgI.sub.2, taken to a temperature lower than, or equal to, that of the sublimation zone. The transfer zone is brought continuously closer to the charge, in proportion to the growth of the mono-crystal. This process is complicated in operation, because it requires the use of a vacuum pump and of a mobile oven, having several windings. Besides, it is difficult to control the different parameters governing the seeding and the growth, so as to obtain mono-crystals without redhibitory structural defects.
Other processes, still more complicated, have been described in French Pat. No. 2,315,994 and U.S. Pat. No. 4,094,268.
There exists, therefore, a need for a process for the production of mono-crystals of good quality and of high purity in a closed chamber, which should be relatively easy to operate, does not require complicated and burdensome equipment and allows for good control of the parameters.
The object of the invention is to provide such a process.